Spectral efficiency provides the ability to transmit data at high speed with a fixed frequency bandwidth. The spectral efficiency is an important parameter for designing wireless communication systems. Orthogonal frequency division multiplexing (OFDM) achieves high spectral efficiency, and has robustness against inter symbol interference (ISI) caused by channel multipath. One major drawback of the OFDM is the high peak-to-average power ratio (PAR) of transmission signals. PC-OFDM has been proposed using parallel combinatory (PC) signaling technique to reduce the PAR, to improve the spectral efficiency, and to reduce the bit-error rate (BER).
High-compaction multicarrier modulation (HC-MCM) has also been proposed to improve the spectral efficiency at the expense of BER performance. The HC-MCM is configured to transmit a truncated version of the OFDM signal. Thus, amplitude discontinuities between two successive signal waveforms appear and result in unnecessary frequency bandwidth expansion.
On the other hand, parallel combinatory HC-MCM (PC/HC-MCM) has been proposed to improve the BER of the HC-MCM and to reduce the PAR. However, the PC/HC-MCM also contains the problem of discontinuities in the waveforms as in the HC-MCM. Thus, it is desirable to reduce the unnecessary frequency bandwidth expansion by preventing amplitude gaps in the PC/HC-MCM signal waveforms.